Temporal expression of SV40 genes occurs in two phases in the lytic cycle. During the early phase, prior to viral DNA replication, early SV40 RNA is synthesized which codes for the early viral T-antigen. Subsequently, late RNA, which codes for the viral structural proteins, is produced in large quantities (5 to 20 times as much as early RNA). The enzymic components responsible for the transition from the early phase to the late phase of the cycle are unclear, but were thought to be linked to viral DNA replication. We have shown, instead that the abundant late transcription depends primarily on the presence of a functional T-antigen. Using the sarkosyl extraction procedure with incorporation of radiolabeled nucleotides into nascent RNA in vitro, we have shown: 1) Virtually all of the RNA synthesized by the supernatant fraction is virus-specific; 2) qualitatively, the RNA synthesized by the sarkosyl pellet fraction is identical to the RNA synthesized by the supernatant; 3) the rate of synthesis of late:early RNA in an extract obtained late in the lytic cycle is approximately 10:1; 4) there is essentially no initiation of transcription of viral sequences in vitro; 5) the method effectively eliminates processing of viral RNA, allowing for an analysis of nascent transcripts. We have considered the possibility that human tumors may contain human papovavirus sequences which may or may not be etiologically related to the disease state. It has been shown, for example, that BKV and JCV, two human papovaviruses, are frequently found in immunodeficient patients, the latter case, in the brains of patients with PML. In addition, BKV has been isolated from a brain tumor of a patient with the Wiskott-Aldrich syndrome. We have been screening human tumor and continuous tissue culture lines derived from human tumors as well as normal human tissues for the presence of homologous sequences. BIBLIOGRAPHIC REFERENCE: Khoury, G. and May, E.: Regulation of early and late SV40 transcription: Dependence of late RNA synthesis on a functional T-antigen. J. Virol., 1977, in press.